The fuel vapor treatment device of this type is disclosed in Japanese Patent Provisional Publication No. 2002-30998 and will be discussed with reference to FIG. 18. The fuel vapor treatment device includes a casing 1 which has a charge port 3 connected to a fuel tank 2, a purge port 3 connected to an intake manifold 5 of an engine 4, and an atmospheric air port communicated with atmospheric air. During stopping of the engine, gas containing fuel vapor (fuel component) is introduced from the charge port 3 into the casing. Fuel vapor adsorbing material 8 such as activated carbon is filled in the casing 1 so as to adsorb or remove fuel vapor in the gas. The gas from which fuel vapor has been removed is released through the atmospheric air port 7 to atmospheric air. When the engine is operated from the above condition, fuel vapor in the fuel vapor adsorbing material 8 is sucked through the purge port 6 into the intake side of the engine to be combusted in the engine. At this time, the fuel vapor in the fuel vapor adsorbing material 8 is purged under the action of atmospheric air introduced through the atmospheric air port 7.
The inside of the casing 1 is divided by a partition wall 9 into a first charging chamber 10 communicated with the charge port 3 and the purge port 6 and a second charging chamber 11 communicated with the atmospheric air port 7. The end sections of the first and second charging chambers 10, 11 are communicated with each other through a communication passage 12 thereby forming a generally U-shaped gas passage within the casing 1. The first charging chamber 10 is defined by oppositely disposed filters 13, 14 and filled with the fuel vapor adsorbing material 8. The second charging chamber 11 is defined by oppositely disposed filters 15, 17, and further divided into two chambers by a filter 16 disposed between the filters 15, 17. The two chambers in the second charging chamber 11 are filled with the fuel vapor adsorbing material 8. Accordingly, fuel vapor introduced through the charge port 3 into the casing 1 is mainly adsorbed by the fuel vapor adsorbing material 8 in the first charging chamber 10, and then the remaining part of the fuel vapor is introduced through the communication passage 12 to the fuel vapor adsorbing material 8 within the second charging chamber 11 to be adsorbed by the fuel vapor adsorbing material 8.
Such a conventional fuel vapor treatment device is provided for the purpose of reducing emission of fuel vapor in the fuel tank into atmospheric air. However, in the recent years, a regulation for emission control of fuel vapor to atmospheric air has become more strict, and therefore it has been required to further lower the emission amount of fuel vapor to atmospheric air. In this regard, it has been known that it is effective to increase a ratio (L/D value) of the length (L) of a layer of the fuel vapor adsorbing material to the diameter (D) of an effective cross-sectional area of the layer in order to reduce emission of fuel vapor to atmospheric air. In this regard, study has been made to increase the L/D value.
In the above conventional fuel vapor treatment device, increasing the L/D value is taken into consideration; however, in order to sufficiently increase the L/D value, a new design for the whole casing of the fuel vapor treatment device is necessary thereby unavoidably increasing a production cost of the fuel vapor treatment device.
Additionally, there is now a requirement of separately producing a plurality of fuel vapor treatment devices which have different specifications to provide different L/D values. To meet this requirement, it is necessary to prepare a plurality of production equipments for separately produce a plurality of different casings, thereby providing the fear of lowering the production efficiency of the fuel vapor treatment devices.